Preview at WWDC likely in June, followed by September launch.
Confirmed: Adobe To Launch CS3 On March 27th [Updated]
The long-awaited suite of creative tools is expected to kick-start Mac Pro sales, and will be the first release of CS3 that is optimised to run natively on Intel-based Macs.
Adobe calls the 27 March announcement "the largest software release in Adobe's 25-year history".
Adobe had previously launched a beta version of Photoshop CS3, which preliminary benchmarks indicated substantial performance gains on Intel based hardware.
The launch date was previously floated by a Merrill Lynch analyst Jay Vleeschhouwer, however AppleInsider also deserves credit for having called an early release as early as October 2006.
Update: According to Adobe's blog, the New York event will indeed unveil more features and specific configurations (presumably including pricing) of the software. However, the site specifically mentions that the software will not ship until later in the spring.